Nonoriented active earth satellite with improved antenna gain



Oct. 3l, 1967 Y. E. STAHLER 3,350,642

NONORIENTED ACTIVE EARTH SATELLITE WITH IMPRovED ANTENNA GAIN Filed sept. 22, 1964 v 6o Y Eigfff'ff \f\` lJ/Ple'xew (26) PIMP se' '/c'a/vrawl. (la) I aan (46) Refine-vee Osc/Larme (4 4) Finn- *Y V a/m/ A777024/ .y BY

United States Patent Once 335,642 Patented Oct. 31, 1967 ABSTRACT OF THE DISCLOSURE This invention relates to an orbital communication relay station which provides antenna gains and operates free of attitude stabilization controls. The antenna gain is achieved by covering the entire surface of the orbiting body with. radiating elements which are cor-rectly phased and properly gated by the information signals from the terminal stations.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to earth-orbiting communications satellites and, particularly, to an earth satellite usefully operating although totally free of attitude stabilization controls.

Active communications satellites generally rely on xed surfaces, jets, gyroscopic and other devices to orient the satellite in a particular attitude' with respect to the earth and thus achieve maximum directivity of the earth-bound wave. Stabilization equipment however imposes a severe drain on the modest primary power aboard the satellite, contributes considerably to the total weight of the satellite, and otherwise introduces complex problems which restrict the span over which the satellite can reliably operate.

Accordingly, one object of the invention is to provide an active communications satellite free of attitude stabilization devices once in orbit.

Another object of the invention is the provision of an active communications satellite that automatically radiates a reply in the direction of the data transmission center requesting a communications link.

Still a further object of the invention is to provide an active 'communications satellite in which the signal contributions back at the inquiring ground station will all be in phase regardless of attitude deviations of the satel- A further object of the invention is the provision of an active communications satellite which has extreme reliability and very high antenna gain.

In accordance with' the invention, an orbiting earth satellite having a more or lessregular surface is provided externally with a plurality of antenna elements arranged in a non-uniform pattern to intercept incoming radiation regardless of the direction of the source. A satellite with a spherical hull appears to be an ideal compromise because, among other things, of the ease with which it lends itself to saturation dispersal of the'antennas. Antennas which are visible to the wave emitted by a particular ground center are coupled into the point-to-point communications link. The convention of stabilizing the satellite prior to data transmission is dismissed by continuously transmitting along with the data signal a pilot frequency which activates those antennas exposed to the transmitting station. A second pilot signal is transmitted simultaneously from a ground station of other global `jidentilication and activates those antennas pointing in its direction. Any variation in the angular position of the satellite produces a continuous procession o-f antennas into and out of the respective radiation streams, always leaving the same number of activated and deactivated antennas and keeping wasteful and misdirected communications transmission to a minimum. Each antenna is connected to an independently sensitive phase-lock circuit, the outputs of which are combined coherently at intermediate frequency and then reradiated, after amplication, to arrive in the far field properly phase-locked for maximum radiation.

Other objects and advantages Will appear hereinafter.

A complete understanding of the invention may be had from the following description when read in conjunction with the accompanying drawings, wherein:

FIG. l is schematic circuit of the preferred form of the invention as applied to a spherical satellite; and

FIG. 2 4is a spherical satellite characterizing the invention, showing one construction and a preferred arrangement of the antennas on the surface of a sphere.

Referring now to FIG. 1, an earth satellite repeater generally referenced 10 for communications purposes comprises a generally spherical body 12 whose hull provides a mounting base for a plurality of antennas 14 and 16 liberally distributed over the surface of body 12 and mounted preferably tiush against the hull so as to eliminate any shadow eifect. Since with proper design more than one frequency can be multiplexed over the same antenna, continuous two-way communications will require at least two antennas of different resonance. Four being the highest number of bandwidths necessary for achieving two-way communication, it will be assumed as the description proceeds that antennas 14 and 16 are designed to accommodate different bandwidths, and that their slight difference in size as depicted in FIG. 1 is intended to represent their use at different wavelengths.

FiG. 2 illustrates in greater detail the preferred external construction of a spherical satellite embodying the invention as Well as one arrangement by which the antennas are made visible from a particular terrestrial point without regard to satellite orientation, In FIG. 2, antennas 14 and 16l are equivalent to antennas 14 and 16, respectively, shown in FIG. 1. In satellite communication systems of the type embodying the invention polarization considerations cannot be ignored since poralization cannot be predicted with utter certainty nor can it be kept constant. To avoid the unpredictable consequences of changing polarization, antennas 14 and 16 may be arranged, as herein shown for example, as crossed dipoles assumed to be operating in phase quadrature in a manner well known in the art. As such, the antenna array covering the face of satellite 1t) will operate with no marked dependence on polarization.

In the most favourable band for space communications, i.e., l kmc. to l0 kmc., the dimension of the dipoles is on the order of centimeters. A satellite hull of several feet in diameter can easily accommodate a large number of dipole elements. As will be obvious, the paired dipoles as shown in FIG. 2 are cut to different lengths because of the diiferent wavelengths over which they opcrate.

From FIG. 2 it will be apparent that the same number of antennas in each group will always be visible from any ground station having the satellite in its field of view. This is true, of course, only so long as the shape of body 12 remains spherical. Therefore, it will be appreciated that the presence of attitude imbalance is of no concern in the spherical array embodying the invention, since transmission between two ground stations will in no way be disrupted. As fast as one antenna moves out of the field of energy arriving from a ground station, another antenna occupying a different part of the spherical surface will replace it.

If desired, the exterior of body 12 in the areas between the crossed dipoles may be Spangled with powergathering solar cells 17. Due to the low silhouette offered by the dipole structure the energy collection is relatively unshadowed so that adequate quantities of self-contained power for long periods of time can be expected.

As indicated in FIG. 1, phase control equipments 18 are mounted within the body 12 of satellite 10 and establish an interior path between each antenna 14 and a repeater which serves exclusively for the reception of signals at the antenna 14 array. In identical fashion, mounted also in body 12 are phase control equipments 22 which establish an interior path between each antenna 16 and a repeater 24 which serves exclusively for the reception of signals at the yantenna 16 array. Power requirements for the phase controls and the repeaters may be met suitably by batteries (not shown) arranged for being charged by solar cells 18 in accordance with accepted practice.

The elements in each phase control 18 function identically as corresponding elements in each phase control 22. The same is true of repeaters 20 and 24. Failure of any one phase control therefore will not affect the operation of the phase controls remaining operative; a high degree of redundancy is thus guaranteed. Accordingly, the elements associated with only phase control 18 will be described. The elements of phase controls 22 wil-l be referenced with accented numbers corresponding identically to the designations applied to corresponding elements Iof phase controls 18.

Phase control 18 includes a suitable diplexer 26 which permits simultaneous reception and transmission of two signals and thus separation of incoming and outgoing signals. Received signals admitted by diplexer 26 are fed to a mixer 28 whose other input is derived from a voltage controlled oscillator (VCO) 30 having an output frequency proportional to an error voltage on line 32. In general, VCOs 30 and 30 incorporated in phase controls 18 and 22, respectively, will be set very close to the carrier frequency of the received modulated signal. The conversion products produced by mixer 28 are fed to a common line 34 of a group including other common lines 36 and 38. As will hereinafter be described, the phase of all intermediate frequency signals on either line 34 or line 34 will be the same.

Continuing with the description of phase control 18, the output of mixer 28 also is applied to a filter 40 which feeds a conventional phase detector 42 which detects both magnitude and sign of the phase angle between two input voltages or currents. The output of phase detecto-r 42 represents an error signal of the correct phase applied over line 32 to control VCO 30. Local oscillator power for phase detectors 42 and 42' is generated in central reference oscillators 44- and 44', respectively, coupled to common lines 36 and 36', respectively. In general, -oscillator 44 will be set very close to the intermediate frequency modulated output of mixer 28. By the same reasoning, oscillator 44 will be set very close to the intermediate frequency modulated output of mixer 28.

The amplitude of the error voltage of phase detector 42 is used to control a gate 46 normally preventing the passage of signals and dependent on the gate signal from phase detector 42 to establish a path between line 38 and a second mixer 48 which receives an oscillatory signal from VCO 30. Mixer 48 is coupled to diplexer 26 and together with gate 46 forms `a path over which intermediate frequency modulated signals transmit-ted by one ground station and incident on the satellite from one direction may be radiated in phase coherence from the satellite in a different direction, that is, toward another ground station.

As seen in FIG. l, respectively, repeaters 20 and 24 comprise filters 50 and 50', amplifiers 52 and S2', and impedance networks 54 and 54. Interior paths through 4 satellite 10 for simultaneously reinforcing two-way communications transmission are therefore established. Filters 5ft and 50 are tuned to suppress all but a predetermined intermediate frequency signal produced by mixe-rs 28 and 28', respectively. Impedance network 54, for example, acts as a transition between the impedance of amplifier 52 and the low impedance caused by the number of parallel transmission paths leading from line 38 to phase controls 22.

In operation, a wave originating from a ground station 60 impinges on those antennas 14 which face it, with other antennas being shadowed by the satellite body. Thus, only those antennas visible to the incident energy will be active. Obvious-ly, this includes roughly one-half the number of the antennas in the spherical array. On the other side of the satellite body, each antenna 16 is depicted as being visible to the wave from a second ground station 62 with whom communication through the satellite is to be established. Confining for the moment the description to one-way communication, -a pilot signal centered at a frequency fp is transmitted by station 60 along with an information-carrying channel transmitted in an adjacent but separate band centered, for example, `at frequency f1. The incoming signals are beat against the signal from VCO 30. As the intermediate frequency pilot signal proceeds through filter 40 it is compared in phase by phase detector 42 with the sign-al from refe-rence oscillator 44. The error voltage on line 32 varies the frequency of VCO 30 in such a way that the intermediate frequency pilot signal and the signal from oscillator 44 yare brought into phase agreement. In other words, the pilot -signal is phase-locked tothe common reference oscillator. Various reasons for such phase angle differences include variations in the angle of arrival of signals incident on satellite 10 and motion of the antenna elements due to tumbling. At the same time, the frequencies of VCO 30 in each phase control 18 having the antenna thereto excited is separately adjusted `according to the phase of the pilot signal. In a manner well known to those skilled in the art, this effectively neutralizes the phase differences between the intermediate frequency modulation signals. The effect at line 34 is that all of the signal contributions thereon will be in phase. This is equivalent to having a directive antenna concentrating maximum energy by looking directly at the source. Thus, by the described arrangement of phase-locking a pilot signal to the output of a common reference oscillator, compensation is made for the differential time delays in the transmission of signals from ground station 60 to the various antennas, and the far field strength of ground station 60 is automatically focused prior to insertion into repeater 20.

The common distribution line 34 feeds into filter 50. Here, all but a predetermined side-band signal'is suppressed. Following amplification in amplifier 52 this signal is now fed to line 38' thus enabling signals from ground stati-on 6ft to be fed to another sector of the satellite on which antennas 16 are activated.

To this end, from ground station 62, the antennas 16 acquire pilot signal, for example, at a frequency fp', transmitted alongside an information-carrying channel occupying an adjacent and separate band centered say, at frequency f2. By the same procedure described hereinabove in connection with actuating gate 46 by the pilot signal fp, the gates 46 will close. This causes antennas 16 to develop a communications signal at a frequency centered, for exam-ple, at f3. The action of each VCO 30 introduces a phase difference in the right amount in the signal f3 from each antenna 16 so that the far field distribution in the vicinity of ground station 62 is essentially in the form of a plane wave. Thus, from no difference in phase angle from the various intermediate frequency components on line 38', the waves when fed to antennas 16 have a phase relationship which gives a plane wave in the far field. It will be noted that such parallel wavefront is propagated retrodirectively to the incident wave fp.

Looking now at gates 46, which have continuously been activated by phase detectors 42 thereby readying antennas 14 for transmission, simultaneous two-way intercontinental transmission with extreme directivity toward both ground stations becomes immediately apparent. In response to the pilot signal fp at antennas 14, VCO 30 displays a phase angle dependent on the error signal output of phase detector 42. As phase detector 42 senses the phase angle difference relative to reference oscillator 44, a similar phase distribution continuously is being imposed on mixer 48 land directly affects the phase of the output signal corresponding to the communications signal f2. It will be recognized that this is the signal summed up on line 34 and repeated in repeater 24. Now split into each gate 46, the phase-coherently added signal is phased in each mixer 48 according to the positions of each excited antenna 14. The individually transmitted components, now say at a carrier frequency f4, converge into a coherent wavefront. Thus, from the point of View of ground station 60, the wave incident thereon is 4an undistorted main beam having every appearance of emanating from 'a single aperture having a high antenna gain.

It will be realized that the invention method of simultaneous continuous transmission of two pilot signals on an orbiting satellite is analogous to tracking an airplane with two huge searchlights that converge at a point somewhere on the airplanes surface. In the present invention the gating and Ipase-locking is performed according to instantaneous distribution and phase excitation of a relatively large number of antenna elements spread evenly over a spherical surface. Accordingly, the individually transmitted beams will have a corresponding phase identification. Thus, as long as a pilot signal from two or more ground stations is focused on the satellite body, a doubly or triply retrodirective system is readily possible depending on the number of ground stations participating.

It will be understood that various changes and modications in the arrangements of the parts which have been described and illustrated in explaining the nature of the invention may be made by those skilled in the art within the spirit of the invention and the scope of the appended claims.

I claim:

1. A space satellite for use as a two-way repeater in a long distance communications system comprising:

an essentially spherical body adapted for orbital flight and communicating between two widely separated earth terminals arranged to irradiate said body simultaneously;

each of said terminals irradiating said body with a modulated signal containing the information to be relayed via said body and a continuous wave pilot signal centered in a band adjacent to but separate from said modulated signal;

a plurality of electrically-isolated and closely packed antennas mounted on the outer surface of said body and being so distributed thereon as to present to each of said terminals roughly one-half the number of said antennas at times when said body is visible to both of said terminals;

said antennas being classified as iirst and second arrays whereby the antennas of said first array are separately and individually excited by the pilotl signal and modulated signal from one terminal, and the antennas of said second array are separately and 6 individually excited by the pilot signal and modulated signal from the other terminal; independently operating phase control means disposed inside said body and coupled to each antenna for reducing essentially to zero all phase angle differences affecting the modulated signal irradiating each array, thereby correcting for different distances between said terminal and the diverse antenna locations on said body;

said excitation of said iirst array establishing through the phase control means connected thereto a rst multiplicity of receiving circuits which terminate in a first common line additively combining the components of the modulated signal on said rst array, and a irst multiplicity of gated transmitting circuits actuated by said pilot signal in the adjacent band to said modulated signal on said iirst array such that only those antennas of said first array excited at a particular moment will be connected for reradiation toward said one earth terminal;

said excitation of said second array establishing through the phase control means connected thereto a second multiplicity of receiving circuits which terminate in a second common line additively combining the components of the modulated signal on said second array, and a second multiplicity of gated transmitting circuits actuated by said pilot signal in the adjacent band to said modulated signal on said second array such that only those antennas of said second array excited at a particular moment Vwill be connected for reradiation toward said other earth terminal;

iirst active repeated means within said body unidirectionally connected between said irst common line and said second multiplicity of transmitting circuits for amplifying the additively combined signal developed by said rst array;

and second active repeater means within said body unidirectionally connected between said second common line and said rst multiplicity of transmitting circuits for amplifying the additively combined signal developed by said second array.

2. In a space statellite as claimed in claim 1, said antennas of each array being arranged as crossed dipoles operated in phase quadrature and the antennas of said first array are of a size to only accommodate the bandwidth from one of said earth terminals and the antennas of said second array are of a size to only accommodate only the bandwidth lfrom said other earth terminal.

3. In a space satellite as claimed in claim 1, a plurality of power-gathering solar cells mounted on the outer surface of said body in the spaces unoccupied by said antennas, said antenna elements being substantially llush mounted on said outer surface of said body to keep shadowing of said solar cells to a minimum.

References Cited UNITED STATES PATENTS 3,151,326 9/1964 Ohm 325-14 X 3,188,640 6/1965 Simon et al. 343-100 3,196,438 7/1965 Kompfner B25-15 X 3,273,151 9/1966 Cutler et al 343--100 JOHN W. CALDWELL, Primary Examiner. DAVID G. REDINBAUGH, Examiner. B, AssistmtwEgamz'ner. 

1. A SPACE SATELLITE FOR USE AS A TWO-WAY REPEATER IN A LONG DISTANCE COMMUNICATIONS SYSTEM COMPRISING: AN ESSENTIALLY SPHERICAL BODY ADAPTED FOR ORBITAL FLIGHT AND COMMUNICATING BETWEEN TWO WIDELY SEPARATED EARTH TERMINALS ARRANGED TO IRRADIATE SAID BODY SIMULTANEOUSLY; EACH OF SAID TERMINALS IRRADIATING SAID BODY WITH A MODULATED SIGNAL CONTAINING THE INFORMATION TO BE RELAYED VIA SAID BODY AND A CONTINUOUS WAVE PILOT SIGNAL CENTERED IN A BAND ADJACENT TO BUT SEPARATE FROM SAID MODULATED SIGNAL; A PLURALITY OF ELECTRICALLY ISOLATED AND CLOSELY PACKED ANTENNAS MOUNTED ON THE OUTER SURFACE OF SAID BODY AND BEING SO DISTRIBUTED THEREON AS TO PRESENT TO EACH OF SAID TERMINALS ROUGHLY ONE-HALF THE NUMBER OF SAID ANTENNAS AT TIMES WHEN SAID BODY IS VISIBLE TO BOTH OF SAID TERMINALS; SAID ANTENNAS BEING CLASSIFIED AS FIRST AND SECOND ARRAYS WHEREBY THE ANTENNAS OF SAID FIRST ARRAY ARE SEPARATELY AND INDIVIDUALLY EXCITED BY THE PILOT SIGNAL AND MODULATED SIGNAL FROM ONE TERMINAL, AND THE ANTENNAS OF SAID SECOND ARRAY ARE SEPARATELY AND INDIVIDUALLY EXCITED BY THE PILOT SIGNAL AND MODULATED SIGNAL FROM THE OTHER TEMINAL; INDEPENDENTLY OPERATING PHASE CONTROL MEANS DISPOSED INDISE SAID BODY AND COUPLED TO EACH ANTENNA FOR REDUCING ESSENTIALLY TO ZERO ALL PHASE ANGLE DIFFERENCES EFFECTING THE MODULATED SIGNAL IRRADIATING EACH ARRAY, THEREBY CORRECTING FOR DIFFERENT DISTANCES BETWEEN SAID TERMINAL AND THE DIVERSE ANTENNA LOCATIONS ON SAID BODY; SAID EXCITATION OF SAID FIRST ARRAY ESTABLISHING THROUGH THE PHASE CONTROL MEANS CONNECTED THERETO A FIRST MULTIPLICITY OF RECEIVING CIRCUITS WHICH TERMINATE IN A FIRST COMMON LINE ADDITIVELY COMBINING THE COMPONENTS OF THE MODULATED SIGNAL ON SAID FIRST ARRAY, AND A FIRST MULTIPLICITY OF GATED TRANSMITTING CIRCUITS ACTUATED BY SAID PILOT SIGNAL IN THE ADJACENT BAND TO SAID MODULATED SIGNAL ON SAID FIRST ARRAY SUCH THAT ONLY THOSE ANTENNAS OF SAID FIRST ARRAY EXCITED AT A PARTICULAR MOMENT WILL BE CONNECTED FOR RERADIATION TOWARD SAID ONE EARTH TERMINAL; SAID EXCITATION OF SAID SECOND ARRAY ESTABLISHING THROUGH THE PHASE CONTROL MEANS CONNECTED THERETO A SECOND MULTIPLICITY OF RECEIVING CIRCUITS WHICH TERMINATE IN A SECOND COMMON LINE ADDITIVELY COMBINING THE COMPONENTS OF THE MODULATED SIGNAL ON SAID SECOND ARRAY, AND A SECOND MULTIPLICITY OF GATED TRANSMITTING CIRCUITS ACTUATED BY SAID PILOT SIGNAL IN THE ADJACENT BAND TO SAID MODULATED SIGNAL ON SAID SECOND ARRAY SUCH THAT ONLY THOSE ANTENNAS OF SAID SECOND ARRAY EXCITED AT A PARTICULAR MOMENT WILL BE CONNECTED FOR RERADIATION TOWARD SAID OTHER EARTH TERMINAL; FIRST ACTIVE REPEATED MEANS WITHIN SAID BODY UNIDIRECTIONALLY CONNECTED BETWEEN SAID FIRST COMMON LINE AND SAID SECOND MULTIPLICITY OF TRANSMITTING CIRCUITS FOR AMPLIFYING THE ADDITIVELY COMBINED SIGNAL DEVELOPED BY SAID FIRST ARRAY; AND SECOND ACTIVE REPEATER MEANS WITHIN SAID BODY UNDIRECTIONALLY CONNECTED BETWEEN SAID SECOND COMMON LINE AND SAID FIRST MULTIPLICITY OF TRANSMITTING CIRCUITS FOR AMPLIFYING THE ADDITIVELY COMBINED SIGNAL DEVELOPER BY SAID SECOND ARRAY. 